For completeness, Table REF  gives results for the number of relativistic species and the sum of neutrino masses for the 12.1HM and 12.5HMcl likelihoods. These results are consistent with those reported in PCP18. Increasing the number
of relativistic species above the value \(N_{\rm eff} = 3.046\)  of the base \(\rm {\Lambda CDM}\)  model has been proposed as a
possible solution of the tension between direct measurements of \(H_0\)  and the value inferred from the CMB [1]}, [2]}. However, it clear from Fig. REF  that this solution is quite strongly disfavoured by Planck. Allowing \(N_{\rm eff}\)  to vary, the 12.5HMcl TTTEEE+BAO+lensing likelihood gives \(N_{\rm eff}=3.01 \pm 0.19\) , \(H_0 = 67.42 \pm 1.25 ~\text{km}~\text{s}^{-1} \text{Mpc}^{-1}\) , i.e. very close to the best fit parameters of the base \(\rm {\Lambda CDM}\)  model, and discrepant by \(3.1 \sigma \)  from the \(H_0\)  determination reported in [3]}.
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